SEATTLE (AP) — For generations, pot crusaders have called for an end to the nation’s prohibition of marijuana, citing everything from what they say are the government’s exaggerated claims about its dangers to the racial disparities in who gets busted for drug possession.

Now, they will get their chance in Colorado and Washington state to show that legalizing pot is better, less costly and more humane than the last 75 years of prohibition — all with the federal government’s blessing.

In a sweeping new policy statement, the Justice Department said Thursday it will not stand in the way of states that want to legalize, tax and regulate marijuana as voters in Washington and Colorado did last fall, as long as there are effective controls to keep marijuana away from kids, the black market and federal property.

“It’s nothing short of historic,” said Dan Riffle of the Marijuana Policy Project, which backed Colorado’s new law. “It’s a very big deal for the DOJ to say that if the states want to legalize marijuana, that’s fine. Everybody in this movement should be thrilled.”

It won’t just be the White House watching to make sure Washington and Colorado get it right. Voters in Oregon and Alaska could weigh marijuana legalization measures next year, and several states could face ballot questions in 2016, activists say.

Meanwhile, Latin and South American countries are also considering pot reform, and the Obama administration’s stance on Washington’s and Colorado’s laws could embolden them, said Ethan Nadelmann, executive director of the New York-based Drug Policy Alliance, which supported Washington’s law. Uruguay has already approved plans to license marijuana growers and shops.

The DOJ’s decision came nearly 10 months after the votes in Washington and Colorado, and officials in those states had been forging ahead to make rules for their new industries without knowing whether the federal government would sue to block sales from ever taking place on the grounds that they conflict with federal law.

Licensed, taxed marijuana sales in the two states are due to start next year, and officials have estimated they could raise tens or hundreds of millions of dollars for state coffers.

The administration’s guidance laid out eight federal law enforcement priorities that states need to protect if they want to authorize “marijuana-related conduct.” They include keeping marijuana in-state, off the black market, and away from children; preventing violence and gun crimes related to marijuana distribution; and preventing drugged driving.

The DOJ noted that it simply doesn’t have the resources to police all violations of federal marijuana law, and so it would focus on entities that threaten those priorities. If a state’s enforcement efforts don’t work, the feds could sue to block the state’s entire pot-regulating scheme, Deputy Attorney General James Cole wrote in a memo to all 94 U.S. attorneys around the country.

The priorities are similar to the factors the Justice Department has previously considered in determining whether to shut down medical marijuana dispensaries. But the memo also clarifies that just because a regulated marijuana operation is big and profitable isn’t reason enough to raid it.

Peter Bensinger, a former head of the Drug Enforcement Administration, criticized the announcement, saying the conflict between federal and state law can’t be reconciled. Federal law is paramount, and Attorney General Eric Holder is “not only abandoning the law, he’s breaking the law,” Bensinger said.

Some in the marijuana-reform community also criticized the memo, noting it did not represent a fundamental change in the law, which would require the approval of Congress.

“It’s like, ‘We’re going to be tolerant of this as long as we feel like it,’” argued Seattle marijuana defense attorney Douglas Hiatt. “Is a new administration just going to come in and shut it down?”

But others pointed to language in the memo they found remarkable coming from the Justice Department: an acknowledgement that a well-designed regulatory system could actually help achieve federal law enforcement goals.

“Indeed, a robust system may affirmatively address those priorities by, for example, implementing effective measures to prevent diversion of marijuana outside of the regulatory system and to other states, prohibiting access to marijuana by minors, and replacing an illicit marijuana trade that funds criminal enterprises with a tightly regulated market in which revenues are tracked and accounted for,” Cole wrote.

A Pew Research Center poll in March found that 60 percent of Americans think the federal government shouldn’t enforce federal marijuana laws in states where its use has been approved. Younger people, who tend to vote more Democratic, are especially prone to that view.

But opponents are worried these moves will lead to more use by young people. Colorado and Washington were states that helped re-elect Obama.

Kevin Sabet, the director of Project Smart Approaches to Marijuana, an anti-legalization group, predicted the new Justice Department policy will accelerate a national discussion about legalization because people will see its harms — including more drugged driving and higher high school dropout rates.

Kristi Kelly, a co-founder of three medical marijuana shops near Denver, said the Justice Department’s action is a step in the right direction.

“We’ve been operating in a gray area for a long time. We’re looking for some sort of concrete assurances that this industry is viable,” she said.